Consumers have traditionally used telephone answering machines to ensure that callers can leave a message when the called party is unable to get to the phone. Recently, consumers have also been turning to an ever increasing number of network-based services to ensure that they get all of their calls. The growing number of subscriptions to call waiting service and call answer service (CAS), both offered today by many local telephone companies, are good examples of this "I've got to get my calls" phenomena.
Call waiting is a custom calling service that uses a short tone or a "click" to let a subscriber know someone else is calling while the subscriber is on the phone. The subscriber can then put the first call "on hold" to talk to the second caller. CAS is a custom calling service that redirects all calls encountering either a ring-no-answer or busy condition to a network voice messaging platform where the caller can record a message for the called party. The called party is then provided with a message waiting indicator in the form of a stutter dial tone or a flashing light on the called party's telephone. The called party, upon detection of this indicator, can dial into the voice messaging platform to retrieve the recorded message from his/her mailbox.
One feature that neither of the foregoing network-based services offers is passive call screening. A subscriber to call waiting service does not presently have the ability to determine the identity of the second caller without actually placing the first call on hold and talking to the second caller. Moreover, consumers are faced with a dilemma when deciding whether to discontinue using a conventional telephone answering machine in favor of call answer service. Although consumers switching to call answer service gain the ability to have callers leave a message upon encountering a busy condition (conventional telephone answering machines only provide callers with this opportunity upon encountering a ring-no-answer condition), they lose all ability to screen their calls.